Q51. Can you join 3 tables with INNER JOIN?
Yes. There's no practical limit (though performance degrades with many joins). ```sql SELECT f.name, d.name AS division, c.name AS country FROM faculty f INNER JOIN divis...
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Q52. Can you join a table to itself?
Yes — **SELF JOIN**. You must use aliases to distinguish the two instances. ```sql SELECT a.name AS employee, b.name AS manager FROM employees a, employees b WHERE a.mana...
Q53. What is true about Cartesian Products?
A Cartesian product occurs when tables are joined **without a condition**. Every row in Table A pairs with every row in Table B: `m × n` rows total. It's usually a bug, b...
Q54. INTERSECTION in relational algebra?
In relational algebra and set theory, the **INTERSECTION** of two sets $A \cap B$ yields only the tuples that appear in **both** relation sets simultaneously. ### SQL Imp...
Q55. UNION in relational algebra?
In relational algebra, the **UNION** of two sets $A \cup B$ combines all distinct tuples from both relations into a single unified relation. ### `UNION` vs `UNION ALL` in...
Q56. UNION vs UNION ALL?
| UNION | UNION ALL | |-------|-----------| | Removes duplicates | Keeps duplicates | | Slower (sort + dedup) | Faster | | Use when uniqueness matters | Use when sets are...
Q57. Which set operator for "searched but didn't buy"?
`MINUS` (Oracle) or `EXCEPT` (PostgreSQL/SQL Server): ```sql SELECT name FROM searchers WHERE product = 'X' EXCEPT SELECT name FROM buyers WHERE product = 'X'; ``` ---
Q58. A SELECT statement whose results are used in filtering the main query is called?
A `SELECT` statement nested inside another SQL statement to supply values for filtering or computation is called a **subquery** (also known as an **inner query** or **nes...
Q59. Subqueries can be nested in...
Subqueries can be nested within virtually every major SQL clause and statement: 1. **`WHERE` Clause**: Filtering candidate rows (`WHERE id IN (SELECT ...)`) 2. **`FROM` C...
Q60. Row comparison operators with subqueries?
`IN`, `ANY`, `ALL`, `EXISTS`, `NOT EXISTS`, and standard comparison operators (`=`, `>`, `=`, ` ALL (SELECT salary FROM employees WHERE dept = 'Sales') WHERE salary > ANY...